The earliest inhabitants of the vale of Elwy lived at the nearby Paleolithic site of Pontnewydd (Bontnewydd), which was excavated from 1978 by a team from the University of Wales, led by Stephen Aldhouse Green.

However, the city is believed to have developed around a sixth-century Celtic monastery founded by Saint Kentigern, and is now home to the small 14th century St Asaph Cathedral.

Two hundred and fifty years later, during the Commonwealth, the building was used to house farm animals: pigs, cattle and horses.

[7] The town applied for the status in competitions held by the British government in 2000 (for the Millennium) and 2002 (Queen's Golden Jubilee) but was unsuccessful.

It was announced on 14 March 2012 that the application was successful, and city status was to be bestowed upon St Asaph alongside Chelmsford and Perth.

In Wales, St Asaph is the smallest by council area, with Bangor a close second at 2.79 sq mi (7.2 km2).

The past few decades have seen the local economy in St Asaph thrive, first with the opening of the A55 road in 1970, which took east–west traffic away from the city, and, more recently, with a business park being built, attracting investment from home and overseas.

In recent years, increasing volumes of traffic on the A525, St Asaph High Street, which links A55 with the Clwyd Valley, Denbigh and Ruthin, have led to severe congestion in the city.

Other annual events in the city include the increasingly popular Woodfest Wales crafts festival in June, the Beat the Bounds charity walk in July and the Gala Day in August.

At the top of the city, in Chester Street is St Winifride's (Roman Catholic) and Bethlehem Chapel (Welsh Presbyterian) in Bronwylfa Square.

A number of famous people have strong links to St Asaph, having been born, raised, lived, worked or died in the city.